1. Field of the Invention
The present invention relates to new water-based coating compositions for the production of stoving lacquers, more particularly for the production of elastic fillers for the coating of car bodies.
2. Description of the Prior Art
In recent years, water-based lacquers and coating compositions have acquired increasing significance in view of increasingly stricter emission guidelines regarding the solvents released during the application of coatings. Although in the meantime water-based coating compositions have been developed for many applications, they often do not attain the high quality level of conventional, solvent-containing coating compositions in regard to resistance to solvents and chemicals and also elasticity (flexibility) and mechanical stability. More particularly, there are still no polyurethane-based coating compositions applied from the aqueous phase which satisfy the stringent practical requirements which elastic fillers for the coating of car bodies are expected to meet in regard to impact strength, resistance to chipping and resistance to water and chemicals.
This applies to GB-PS 1,444,933, EP-A-0,061,628 and DE-AS 2,359,613, which are concerned with the hydrophilic modification of aromatic polyisocyanates; DE-OS 4,001,783, which is concerned with special anionically modified aliphatic polyisocyanates; and also to the systems according to DE-OS 2,456,469, DE-OS 2,814,815, EP-A-O,012,348 and EP-A-0,424,697, which are concerned with water-based binders for stoving lacquers based on blocked polyisocyanates and organic polyhydroxyl compounds. The systems based on carboxy-functional polyurethane prepolymers containing blocked isocyanate groups according to DE-OS 2,708,611 and the highly functional, blocked water-soluble urethane prepolymers according to DE-OS 3,234,590 are mostly unsuitable for the production of flexible coatings.
It has now been found that stoving fillers which can be applied from aqueous phase and which satisfy the requirements stated above can be produced, provided that selected combinations of the type described in more detail hereinafter of a) water-soluble or water-dispersible polyhydroxyl compounds containing special water-soluble or water-dispersible blocked polyisocyanates b) are used as binders.